Bonding wire for semiconductor devices

Abstract

There is provided a novel Cu bonding wire that achieves a favorable FAB shape and achieve a favorable bond reliability of the 2nd bonding part even in a rigorous high-temperature environment. The bonding wire for semiconductor devices includes a core material of Cu or Cu alloy, and a coating layer having a total concentration of Pd and Ni of 90 atomic % or more formed on a surface of the core material. The bonding wire is characterized in that: in a concentration profile in a depth direction of the wire obtained by performing measurement using Auger electron spectroscopy (AES) so that the number of measurement points in the depth direction is 50 or more for the coating layer, a thickness of the coating layer is 10 nm or more and 130 nm or less, an average value X is 0.2 or more and 35.0 or less where X is defined as an average value of a ratio of a Pd concentration C Pd (atomic %) to an Ni concentration C Ni (atomic %), C Pd /C Ni , for all measurement points in the coating layer, the total number of measurement points in the coating layer whose absolute deviation from the average value X is 0.3X or less is 50% or more relative to the total number of measurement points in the coating layer, and the bonding wire satisfies at least one of following conditions (i) and (ii): (i) a concentration of In relative to the entire wire is 1 ppm by mass or more and 100 ppm by mass or less; and (ii) a concentration of Ag relative to the entire wire is 1 ppm by mass or more and 500 ppm by mass or less.

The invention claimed is: 
     
       1. A bonding wire for semiconductor devices, the bonding wire comprising:
 a core material of Cu or Cu alloy; and 
 a coating layer having a total concentration of Pd and Ni of 90 atomic % or more formed on a surface of the core material, wherein 
 in a concentration profile in a depth direction of the wire obtained by performing measurement using Auger electron spectroscopy (AES) so that the number of measurement points in the depth direction is 50 or more for the coating layer, 
 a thickness of the coating layer is 10 nm or more and 130 nm or less, 
 an average value X is 0.2 or more and 35.0 or less where X is defined as an average value of a ratio of a Pd concentration C Pd  (atomic %) to an Ni concentration C Ni  (atomic %), C Pd /C Ni , for all measurement points in the coating layer, 
 a total number of measurement points in the coating layer whose absolute deviation from the average value X is 0.3X or less is 50% or more relative to a total number of measurement points in the coating layer, and 
 the bonding wire satisfies at least one of the following conditions (i) and (ii): 
 (i) a concentration of In relative to the entire wire is 1 ppm by mass or more and 100 ppm by mass or less; and 
 (ii) a concentration of Ag relative to the entire wire is 1 ppm by mass or more and 500 ppm by mass or less. 
 
     
     
       2. The bonding wire according to  claim 1 , wherein the total number of measurement points in the coating layer whose absolute deviation from the average value X is 0.2X or less is 50% or more relative to the total number of measurement points in the coating layer. 
     
     
       3. The bonding wire according to  claim 1 , wherein when linearly approximating C Pd  or C Ni  by the method of least squares for all measurement points in the coating layer, a difference between a maximum value and a minimum value of the obtained approximate straight line in a depth range of the coating layer is 20 atomic % or less. 
     
     
       4. The bonding wire according to  claim 1 , wherein the concentration profile in the depth direction of the wire is obtained by performing the measurement using AES under the following <Condition> while digging down the wire from its surface in the depth direction by Ar sputtering:
 <Condition> a center of width of a measuring surface is aligned with a center of width of the wire, the width of the measuring surface is 5% or more and 15% or less of a diameter of the wire, and a length of the measuring surface is five times the width of the measuring surface. 
 
     
     
       5. The bonding wire according to  claim 1 , wherein the bonding wire contains Au at a surface thereof. 
     
     
       6. The bonding wire according to  claim 5 , wherein a concentration of Au at the surface of the wire is 10 atomic % or more and 90 atomic % or less. 
     
     
       7. The bonding wire according to  claim 6 , wherein the concentration of Au at the surface of the wire is measured using AES under the following <Condition>:
 <Condition> a center of width of a measuring surface is aligned with a center of width of the wire, the width of the measuring surface is 5% or more and 15% or less of a diameter of the wire, and a length of the measuring surface is five times the width of the measuring surface. 
 
     
     
       8. The bonding wire according to  claim 1 , wherein when forming a free air ball (FAB: Free Air Ball) by using the wire and then measuring crystal orientations in a cross-section of the FAB perpendicular to a compression-bonding direction, a proportion of a crystal orientation <100> angled at 15° or less to the compression-bonding direction is 30% or more. 
     
     
       9. The bonding wire according to  claim 8 , wherein the proportion of the crystal orientation <100> angled at 15° or less to the compression-bonding direction is 50% or more. 
     
     
       10. The bonding wire according to  claim 1 , wherein
 the bonding wire contains one or more elements selected from the group consisting of B, P and Mg (hereinafter referred to as a “first additive element”), and 
 a total concentration of the first additive element is 1 ppm by mass or more and 100 ppm by mass or less relative to the entire wire. 
 
     
     
       11. The bonding wire according to  claim 1 , wherein
 the bonding wire contains one or more elements selected from the group consisting of Se, Te, As and Sb (hereinafter referred to as a “second additive element”), and 
 a total concentration of the second additive element is 1 ppm by mass or more and 100 ppm by mass or less relative to the entire wire. 
 
     
     
       12. The bonding wire according to  claim 1 , wherein
 the bonding wire contains one or more elements selected from the group consisting of Ga and Ge (hereinafter referred to as a “third additive element”), and 
 a total concentration of the third additive element is 0.011% by mass or more and 1.5% by mass or less relative to the entire wire. 
 
     
     
       13. A semiconductor device comprising the bonding wire according to  claim 1 .